Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 161540 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1140 AM EDT Wed Aug 16 2017 .SYNOPSIS... An area of high pressure will build into the region through tonight. A warm front will move northward Thursday into Thursday night followed by a cold front that should pass through the region Friday night into early Saturday. Weak high pressure will build into the area during the rest of the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... All fog has dissipated and rest of day should generally be tranquil. Ridge of surface high pressure moving eastward from the Great Lakes will crest near the region this afternoon. This will provide for mainly dry conditions and partly-mostly sunny skies. Guidance continues to hint that there may be a spotty shower or t-storm, but the vast majority of the area is not expected to see any measurable rainfall, so at this point have kept pops just below 15 percent. Temperatures should still reach the upper 80s to locally near 90F by late in the afternoon. && .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/... For tonight, surface high will be slow to exit so another night of light winds and mostly clear skies will be in store to start. We`ll be one day removed from significant rainfall however, so while areas of fog and stratus are likely again, coverage/density should be less than this morning. Another factor may be an increase in mid clouds late tonght as the next system approaches, so bottom line is that we are not expecting another dense fog event. Lows from the mid 60s to low 70s. High pressure shifts offshore for Thursday allowing for the return of southerly flow. As an approaching low pressure system lifts through the Great Lakes, a warm front will lift northward and into the region by Thursday afternoon. This and a developing area of broad low level convergence will serve as a focus for shower/thunderstorm development on Thursday. MLCAPE south/west of the warm front is currently progged to be in the 1000-2000 J/KG range, which is quite sufficient for thunderstorm development. Further examination of the modeled forecast soundings would indicate potential for both an isolated severe and isolated flood threat, with the presence of a low level boundary, directional shear along the boundary, 0-6KM shear of around 30 knots, and precipitable water values 2-2.25 inches. Initial focus likely to be west of I-95, with propagation eastward during the evening/overnight hours. Highs Thursday should reach into the mid/upper 80s, with lows Thursday night in the low to mid 70s. The area of low pressure will push into southern Canada on Friday, with its trailing cold front entering the Mid-Atlantic states during the day. This will serve as another focus for scattered showers/thunderstorms during the day Friday. A potential severe threat will exist again on Friday, as temperatures and low level moisture surge out ahead of the front, leading to the development of 1500-2500 J/KG of MLCAPE, with 30-35 knots of shear moving overhead. Highs upper 80s to around 90F. Convection will wane Friday night. && .LONG TERM /SATURDAY THROUGH TUESDAY/... Weak high pressure will build toward the area for Saturday and Sunday. Most areas will remain dry with less humidity. However...a pressure trough will likely be hung up near the Chesapeake Bay into southern Maryland. Humidity may remain across these areas along with an isolated shower/t-storm...but much of the time will be dry. High pressure will move offshore for Monday and Tuesday. Hotter and more humid conditions are expected. && .AVIATION /16Z WEDNESDAY THROUGH SUNDAY/... Conditions VFR rest of today under high pressure. Potential for additional fog/stratus exists tonight, although coverage/density should be less than this morning. Next weather concerns will be the possibility of scattered showers/thunderstorms both Thursday and Friday, where brief reductions of both ceiling/visibility are possible. High pressure should bring VFR conditions most of the time for Saturday and Sunday. && .MARINE... Sub-SCA conditions expected through Thursday. South winds will then be on the increase late Thursday through Friday ahead of a frontal system, and Small Craft Advisory conditions are expected across the middle portion of the bay and lower tidal Potomac. Have issued SCA for late Thursday-Thursday night period, and this will likely need to be extended through Friday. Isolated to scattered showers and thunderstorms are also possible both Thursday and Friday, mainly in the afternoon/evening, and Special Marine Warnings may be necessary. A pressure trough will remain near the waters during the weekend. Wind speeds should be below SCA criteria for the most part since the gradient will be week. A return flow from the south will develop early next week as high pressure moves offshore. && .TIDES/COASTAL FLOODING... A light northerly flow allowed anomalies to drop this morning. However...southerly winds will increase for Thursday through Friday night ahead of a cold front. Minor tidal flooding is possible near high tide Thursday night into Friday morning and again Friday night into Saturday morning for sensitive areas. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 4 PM Thursday to 6 AM EDT Friday for ANZ533-534-537-541-543. && $$ SYNOPSIS...BJL NEAR TERM...MM/RCM SHORT TERM...MM/RCM LONG TERM...BJL AVIATION...BJL/MM/RCM MARINE...BJL/MM/RCM TIDES/COASTAL FLOODING...BJL/RCM

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